Tailored and universal parallel transmit broadband pulses for homogeneous 3D excitation of the human heart at 7T.

To research and evaluate the performance of broadband tailored kT-point pulses (TP) and universal pulses (UP) for homogeneous excitation of the human heart at 7T. Relative 3D B 1 + $$ {\mathrm{B}}_1^{+} $$ -maps of the thorax were acquired from 29 healthy volunteers. TP and UP were designed using the small-tip-angle approximation for a different composition of up to seven resonance frequencies. TP were computed for each of the 29 B 1 + $$ {\mathrm{B}}_1^{+} $$ -maps, and UPs were calculated using 22 B 1 + $$ {\mathrm{B}}_1^{+} $$ -maps and tested in seven testcases. The performance of the pulses was analyzed using the coefficient of variation (CV) in the 3D heart volumes. The 3D gradient-echo (GRE) scans were acquired for the seven testcases to qualitatively validate the B 1 + $$ {\mathrm{B}}_1^{+} $$ -predictions. Single- and double-frequency optimized pulses achieved homogeneity in flip angle (FA) for the frequencies they were optimized for, while the broadband pulses achieved uniformity in FA across a 1300 Hz frequency range. Broadband TP and UP can be used for homogeneous excitation of the heart volume across a 1300 Hz frequency range, including the water and the main six fat peaks, or with longer pulse durations and higher FAs for a smaller transmit bandwidth. Moreover, despite large inter-volunteer variations, broadband UP can be used for calibration-free 3D heart FA homogenization in time-critical situations. © 2024 Physikalisch-Technische Bundesanstalt. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.

Citation

Christoph Stefan Aigner, Sebastian Dietrich-Conzelmann, Max Lutz, Felix Krüger, Sebastian Schmitter. Tailored and universal parallel transmit broadband pulses for homogeneous 3D excitation of the human heart at 7T. Magnetic resonance in medicine. 2024 Mar 05

PMID: 38440957

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